The present invention relates to hair analysis and, more particularly, but not exclusively to a method and an apparatus for analyzing hair mixtures and predicting a final color when hair dyeing.
Hair dyes and bleach are used to make gray hairs less conspicuous or to dye hair a desired color. Hair dyes include temporary dyes (color shampoo, color conditioner, color treatment conditioner, etc.) that are easy to apply, the color remaining for a short time, semi-permanent dyes (hair manicure, clear-type hair manicure, etc.) that provide a dye effect that can be continuously maintained through penetration of an acidic dye into the interior of the hair, and permanent dyes that achieve an essentially permanent dye effect through oxidative polymerization of the dye in the interior of the hair. A particular type of hair dye is selected depending on the intended use.
Each of these types of dyes is prepared in numerous color numbers. Usually, each dye color is indicated on the box containing the dye, or by means of sample tresses of dyed hair.
However, even where the same color dye is used, the color of the hair after dyeing differs considerably depending on the color mixture of the hair before dyeing.
In case that the hair before dyeing has a non homogenous mixture of white hair and colored hair, the result, of current methods fail to accurately predict the hair color after dyeing. Colored hair can be natural pigmented hair or dyed with artificial colors.
Consequently, it is difficult to predict the color that will result from dyeing any person's hair solely from the printing on the box or the sample tresses, and the problem arises that the actual color of the hair after dyeing is different from the color anticipated.
There are methods to predict the final hair color in order to minimize error and increase customer satisfaction with the use of hair color products.
Some methods use a color chart or an indexed table which predicts the hair's final color after choosing the initial color from the table and the color to use. For example, U.S. patent application Ser. No. 4,434,467, entitled “Hair coloring calculator” to Scott, filed on Mar. 30, 1981 describes a device for determining the hair coloring products to be used to change the user's present hair color to a new hair color. The device includes a keyboard for entering a designation which identifies the user's present hair color and the desired hair color. The user also enters data to identify the particular line of hair coloring products which the user desires to use. The device then responds to such data by displaying the designations of hair coloring products of the chosen line which will presumably change the user's present hair color to the new hair color.
However, the Scott method and similar methods are restricted to a limited number of possibilities of initial hair colors and therefore fail to predict the exact final color to all variants of initial hairs. Furthermore, the lack of some kind of direct measurement of the customer's initial hair leaves the initial color estimation for the human eye, and prevents the methods from accurately predicting the resulting color.
U.S. patent application Ser. No. 10/473,627, entitled “Hair color measurement and treatment”, to Grossinger et al, filed on Oct. 1, 2003, introduces a way to predict the spectrum of the hair reached after a dyeing process based on the initial spectrum of the hair. An underlying assumption is that the initial hair color is homogenous.
A problem emerges in that when measuring reflectances both the regular natural hair and the white hair are measured together. Thus, the reflectance spectrum received from the measurement device is a combination of both the regular and white hair. The combined spectrum is thus merely a combination of the two hair types in the measured hair and therefore may cause inaccurate final color prediction.
Other known methods perform a measurement of the initial hair color using a colorimeter of some kind (RGB or L, a, b color values which are standard methods to define color). These other methods may also be used to predict the hair color using mathematical equations that are constructed based on a database of colored hairs (U.S. Pat. No. 6,707,929) or on a color table built on a database of the same kind (U.S. Pat. Nos. 6,067,504, 6,157,445, 6,308,088, 6,314,372 and 6,330,341 to MacFarlane, et el).
However the above methods restrict themselves to the color coordinates which are not very representative of the spectrum and thus they lose accuracy and the ability to indicate on the chemical composition of the hair. For example, US Patent Publication No. 2005/0036677, entitled “Advanced cosmetic color analysis system and methods therefore” to Ladjevardi, filed on Feb. 17, 2005 describes a way to analyze the different colors in a measurement of an area of hair.
The measurement as described by Ladjevardi is taken using a digital camera which produces results in the form of a matrix of RGB values. The analysis is performed by iterating through the RGB matrix and sorting its values into some predetermined groups.
The output of the Ladjevardi method may be the concentration of each color group in the measured area. The predetermined groups are verified by a representative RGB value for each one. Presumably, since one can predetermine one group to represent white hair color, this method may be used to analyze the white hair concentration in a given hair sample.
However, since Ladjevardi's method uses RGB values as input it is limited by the resolution of the RGB. As a result of the resolution limit, each pixel in the picture generated by the camera, providing the RGB values, actually consists of a mixture of colors. The underlying mixed pure hair color spectrums are never taken into consideration.
The resolution of the RGB cannot accurately predict the final color of the hair since different spectrums which result from different pigment concentrations can produce the same RGB or L, a, b values but will react differently when treated with bleaching or dyeing agents.
Furthermore, it is known that two different hair samples with different spectrums and pigment structure may have the same color L, a, b coordinates but react differently to bleaching and color treatments.
For example, two samples of hair, which look substantially the same to the human eye may have the same L, a, b color coordinate values even though they have different spectrums of reflectance, and therefore, different concentrations of components (eumelanin pigments, Pheomelanin pigments, artificial hair color, etc).
For example, one natural blond hair sample which is colored with dye A, may have the same color coordinates as another hair sample, say, a brown hair colored with a dye B.
Moreover, a large number of hair samples, each having different reflectance spectra, may all generate the same L, a, b color coordinate values or very similar color L, a, b coordinate values. That is to say, the hair samples having different combinations of Eumelanin, Pheomelanin and keratin concentrations that result in different curves of spectrums, may produce similar color coordinate values.
However, the same hair treatment applied to these hair samples generates different final hair colors due to the different initial concentrations of each of the above materials in each of the hair samples.
As described hereinabove, currently used methods, as discussed above, fail to deal with the subject of predicting the final color of hair that contains two or more hair types with different colors. Ladjevardi deals with this problem but can only produce RGB values of each hair type, thus cannot be use with advanced color prediction methods that uses the full spectral information as input.
There is thus a widely recognized need for, and it would be highly advantageous to have, an apparatus and method devoid of the above limitations.